The present invention relates to an annual calendar device including a date ring bearing thirty-one numbers, which appear in succession through an aperture, said ring carrying thirty-one inner teeth located on a first level, a drive wheel for the date ring completing one revolution in twenty-four hours, and a mechanism (10) carried by said wheel (5) and rotating therewith, said mechanism (10) having a first finger, which, at the end of each day, drives one tooth of the date ring through one step.
An “annual calendar device” means a system which moves the date ring forward one additional step at the end of months having less than thirty-one days, with a manual correction remaining to be performed at the end of February. This correction is automatically performed in timepieces fitted with a so-called perpetual calendar device. Annual calendar devices are disclosed in the horological literature and, by way of example, EP Patent No. 1 666 991 will be cited here, the operation of which is summarized below.
The annual calendar mechanism disclosed in the aforecited document includes a drive wheel for the date ring, fitted with a first finger which drives a date ring once per day, and a second finger, which, at the end of months of less than thirty-one days, drives a plate with five catches secured to an annual wheel, which is arranged coaxially to the date ring. An intermediate wheel connects the annual wheel to the date ring at the end of each month. The annual wheel includes twice as many teeth as there are months in the year and the intermediate wheel includes a first wheel in mesh with the annual wheel and a second wheel fixed to the first. Said second wheel is in mesh, at the end of each month, with a catch placed inside the date ring.
From the foregoing, it will be clear that although the first finger, integrated in the drive wheel, directly drives the date ring each day, the second finger, also integrated in the drive wheel, only drives the date ring indirectly, via a kinematic chain comprising a plate with five catches, an annual wheel and an intermediate wheel formed of two superposed wheels. Said intermediate wheel finally drives the date ring through one additional step at the end of months having less than thirty-one days. It will be clear that this kinematic chain uses energy and that a considerable saving could be made if the second finger, also mounted on the drive wheel, could drive the date ring directly, with no intermediate part, at the end of months of less than thirty-one days. It is an object of the present invention to make this saving.